Integrated circuits include many active devices in an integrated circuit substrate such as a semiconductor substrate. These active devices are generally isolated from one another. Accordingly, isolation structures and methods are widely used in integrated circuits. One important isolation structure and method is a trench isolation structure and method.
Conventional trench isolation structures are fabricated by forming a trench in an integrated circuit substrate and forming an isolation region of insulating material in the trench. Trench isolation structures and methods are described in U.S. Pat. No. 5,387,538 to Moslehi entitled "Method of Fabrication of Integrated Circuit Isolation Structure" and U.S. Pat. No. 5,447,884 to Fahey et al. entitled "Shallow Trench Isolation With Thin Nitride Liner".
In a conventional trench isolation method, a predetermined region of an integrated circuit substrate such as a semiconductor substrate is etched to form a trench region, generally having a quadrilateral section, and an isolation film made of insulating material is formed in the trench region. Then, a process is performed to oxidize the trench sidewalls or to densify an insulating material filled in the trench region. This process is performed to cure damage generated during etching to form the trench.
Unfortunately, in this process, stress may be generated due to a difference in thermal expansion coefficient between the isolation film and the substrate. The stress may be concentrated in the semiconductor substrate around the isolation film, and especially at the comers of the trench. The accumulated stress in the substrate causes crystal defects such as dislocation in the substrate. Such defects may cause an increase in junction leakage currents of the integrated circuit devices. The increased leakage currents may adversely impact performance and/or reliability of the devices.